Support nullable `fromJson`

[TekExplorer]

I have a type I get from a php project, which looks a bit like this:

{
  "object": "user",
  "attributes": {...}
}

And sometimes, that object can be nested

{
  "object": "user",
  "attributes": {
    "thing": {
      "object": "item"
      "attributes": {...}
    }
  }
}

This is fine.

What isnt fine, however, is the null_resource object, which looks like this:

{
  "object": "null_resource",
  "attributes": null // <<<<<<<<<<
}

uh oh. I dont want two layers of null!